Apparatus for treating carbonaceous solids



Aug. 19, 19 2 H. z. MARTIN 2,607,565

APPARATUS FOR TREATING CARBONACEOUS SOLIDS Original Filed Sept. 28, 1946 FRESH l PO'IWDEQED COAL IO 2O 3T2 IPP/NG I: STEAM 1'.-

3 L'J-ilii I u Patented Aug. 19, 1952 APPARATUS FOR TREATING CARBONA- CEOUS SOLIDS Homer Z. Martin, Cranford, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Original application September 28, 1946, Serial No. 699,949. Divided and this application December 23, 1949, Serial No. 134,822

2 Claims. (Cl. 48-452) The present inventionrelates to the conversion of carbonaceous solids into volatile products by carbonization and/or gasification with oxidizing gases and/or steam. More particularly, the invention is concerned-with the pretreatment of carbonaceous solids such as all types of coal, lignite, cellulosic materials, including vlignin, oil shale, tar sands, coke, oil coke, etc. which are to be converted into volatile products by carbonization and/or'gasi'fication or any'other conversion process requiring. a pretreated carbonaceous charge.

I-Ieretofore, it has been customary to pretreat the carbonaceous charge for solid fuel conversion processes by preheating and, in some cases, by a limited oxidation at suitable temperaturespreferably just below the point of beginning softening or volatilization of the charge. For instance, carbonization coal is 'usually'preheated to temperatures varying from about 500 to about 1000 F. depending on the character of the coal and the conditions of the subsequent conversion process. The conventional method of generating and supplying this preheat to the coal'involves the combustion of combustible gases with air in a separate heater and passage of the hot flue gases over the coal to be preheated.

In order to avoid losses of volatile coal constituents and to prevent baking and sticking of the coal in the preheating zone, the inlet temperature of the gas must not exceed about 1000- 1400 F. In addition, the specific heat of the flue gas is only a small fraction of that of the coal to be heated. As a result, the coal must be preheated to an undesirably high temperature and thereafter quenched to the desired temperature or vast amounts of flue gases are required to heat coal of atmospheric temperature up to a desirable preheating temperature of about 500- 700 F. However, even the use ofan extremely large Volume of heating gas of relatively low temperature necessarily entails an irregular distribution of the preheat throughout the coal charge. As the result of channelling effects and due to the low heat transfer coeflicient of the solid charge, the coal first or most intimately contacted by the gas reaches a higher temperature than that contacted later or more incompletely. These conditions not only constitute a serious load on process economies but frequently cause even serious operational difliculties,

The present invention overcomes the-aforementioned difliculties and alfords various additional advantages. These advantages, the nature of the invention and the manner in which it is carried out will be fully understood from the following description thereof read with reference to the accompanying drawing.

It is, therefore, the principal object of my invention to provide improved means for pretreating carbonaceous solids to be subjected to a conversion into volatile products at elevated temperatures. L

Another object of my invention isto provide an improved method and apparatus for uniformly preheating carbonaceous solids .to a definite desired temperature, preliminary to a high temperature treatment of said solids.

A more specific object of my invention is to provide improved means for pretreating, particularly preheating carbonizable solids at uniform temperature below the temperature of beginning softening and carbonization..

Other and more specific objects and advantages of my inventionwill appear-hereinafter.

In accordance with my invention, the carbonaceous solids to be pretreated are maintained in the form of a dense turbulent bed'of finely divided solids fluidized by an upwardly flowing gas and the heat required forthe desired pretreatment is generated in a combustion zone surrounded by and in open communicationwith said bed so as to permit circulation of carbonaceous solids through said combination zone from and to said fluidized bed of solids and'of combustion products from said combustion zone to said fluidized bed.

In this manner, the heat generated by the combustion is immediately transferred to a portion of the carbonaceous solids which serve as solid heat carrier of high specific heat. thus reducing to a minimum the volume of hot flue gases required for pretreating. In addition; the excellent heat transfer and distribution characteristics of the dense'turbulent fluidized bed of solids to "be pretreated and the direct heat exchange between the combustion zone and the fluidized solids bed make it possible to maintain a temperature differential as low as about -400 F. between the heat-generating combustion and the fluidized solids bed to be heated, resulting in the elimination of undesired high temperature side reactions. The pretreated carbonaceous solids are recovered in the form of fluidized or fluidizable solids and are, as such, particularly suitable as charge for conversion processes employing the fluid solids technique. T

The combustion zone may be operated so as to generate merely the heat required for preheating. However, by'a suitable choice of the temperature The fuel burnt in the combustion zone prefer' ably consists of combustible constituents of the.

carbonaceous solids circulated therethroughfrom the dense fluidized mass of solids to be pretreated. 7

However, if it is desired to avoid a lossof come bustible constituents of the solid: carbonaceous charge, an extraneous fuel of lower ignition temperature such as a fuel gas or fuel oilmay be charged to the combustion zone alo'ngwith t air and/or oxygen supporting the combustion. if these fuels are added in theoretical or slightescess proportion to the oxygen sup-plied, little or no combustible constituents of the solid carboe naceouschargewill be burnt and. the latter will act mainly as a heat carrier.

' Having set forth the general nature and ob jects, the invention will be best understood from the more "detailed description hereinafter, in which reference will be made to the accompanying drawing which illustrates semi-diagrammatically a system suitable for carrying. out a .In operation, finely divided bituminous carbonizatioricoal having'a volatile content of about 20 to 35%, a plasticizing temperature of about 700 F. anda temperature of. incipient carbonizetion of about'750f F. is supplied throughpipe l to pretreatingchamber' I0. The coal should have a fluidizable particle size which may fall within I the broad range of about 50400 mesh, 100-200 mesh being preferred, though larger sizes up to about in. maybe used. Pipe 1 may be part i mentioned. may be treated for the same or dif- 1 ferent purposes in a. generally analogous manner.

of any conventional feeding devicefor fluidizable j solids such as an aerated standpipe, pressurized feed. hopper, mechanical conveyor or the like. The finely divided coal forms in chamber iii a dense turbulent bed 20 of solids fluidized by upwardly flowing gases to resemble a boiling liquid having a well defined upper level L10 as'will appear more clearly hereinafter.

Chamber lflis equipped, in its lower portion, with a horizontal plate I2 provided With'pref erably adjustable orifices M which permit a controlled passage of finely divided coal from bed 20 to a point below the bottom of combustion zone 30. A fluidizing gas such. as steam, flue gas, or the like is introduced into bed 20. through several, preferably annular, perforated tubes l located above and in close proximity to plate I2. is preferably so controlled that the gas has a linear velocity of about 0.3-3 ft., preferably about 1-2 ft. per second within bed 20 to convert the latter into the desired dense ebullient mass of The amount of fluidizing gas thus supplied 4 solids. The fluidizing gas may simultaneously serve as a stripping agent to remove occluded undesirable gases from the solids to be passed to combustion zone 30 as will be presently explained. Coal particles passing through orifices is in plate [2 into lower zone 25 of chamber 10 are aerated and kept in a mobile turbulent state by an aeration gas such as air, oxygen, steam, fiue gas, or the like supplied through taps 13 at a linear velocity of about 0.3-3 ft. per second. The 'bulk'of the air and/or oxygen required for combustion is introduced through line directly into the lower, 'open end of combustion zone 30 at a relatively high superficial velocity of about 3-20 ft..per second, so as to establish an ejector effect at the bottom (it zone 30, whereby coal particles are forced intoand upwardly through combustion zone 30. The upper end of combustion zone 30 is preferably provided with a perforated cover plate 30 which permits the passage of solids and gaseous combustion.v products. from. combustion zone 32 into bed, 20 Whileeffectively preventing solids. from entering the top ,of combustion zone 30.. I a

The. temperature of combustion zone 30, may be controlled by: the;,oxygen. content and. linear velocity of the gas supplied through line: 5, the latterdetermining in combination with the open-'- ing of orifices M, the rate. of. fuel supplyto zone 30. For, the purpose of preheating coal bed. 20 to about 600 F. the; temperature in zone 3.0. is maintained at about 800-1000 F. The amount of air required may vary within wide limits; de-

pending'on the relative sizes of; chamberlfll and zone 30, the character of the carbonaoejouscharge and the pretreatment desired; For. the preheat.- ing of coalas indicated aboveina system wherein the ratio of the diameters. ofjchamber. H1 and zone 30 falls within thegapproximate range of 2-10z1, about 0.1 to 5"cu. ft. of air supplied at a linear velocity of about4-10 ft. per second in zone 30 is generallyadequate to preheat 1. lb. ofcoal from about 60 about600 F; The solids-in-gas suspension within combustion zone 30' may; have an apparent density of, abput 1, to lbs; per cu. ft. as compared with. a density of about to 30 lbs; per'cu; ft. of bed- 20.- At these conditions about 0.005; to 0.01- lbs; of combustible coal constituents; are'burnt in zone. 30 per lb. ofrcoal to be preheated.

A dilute suspension of. solid combustion. residue in flue gases passes through cover plate 32 at the temperature of combustion zone: 39 and entersv the fluidized bed which absorbs. the sensible heat of the combustion products uni.- formly through itsentirev mass to attain the desired uniform temperature of about 600 F; It should be understood that the; pseudo-hydrostatic; pressure I generated by the fluidized solids column between plate [1-2 and the top of zone. must begreat enough to overcome the flow resistance through orifices l4, combustion zone 30 and perforated plate 32-. On the other, hand, the length and cross-section of combustionzone 30 should only be fractions. of those of chamber so that the bulk of the treatment of carbonaceous charge takes place within bed 20; In general, the ratioof the heights of vessels i0 and 30 may be about 2-1021, preferably about 8: 1, and the ratio of their diameters-about 2-1011, preferably about 511. "1 w Spent flue gases are withdrawn overhead from level L10 and passed. through line. I to the at"- mosphereor any desiredmse, such 'a'sheat recovery, aeration, etc-.,' if desired, after separation and return to bed 20, .of entrained solids fines by means of a conventional gas-solids separation system including cyclones and/or electrical precipitators, or the like. Preheated fluidized coal is withdrawn from bed 20 through a conventional standpipe 9 or any other conventional conveying means for fluidized solids and passed substantially at the temperature of bed 20 to any subsequent processing stage such as carbonization, producer or water gas manufacture, etc.

If desired, an extraneous fuel, preferably a fuel gas or fuel oil may be introduced through line 35 into air pipe 5 at a point close to its entrance into combustion zone 30. This extraneous fuel supply may be so controlled that it consumes substantially all of the oxygen available for combustion leaving the combustible constituents of the carbonaceous solids entering zone 30 unburnt.

It will be understood that the temperature levels at which zone 30 and bed 20 are operated may be substantially higher or lower than those indicated above. For example, zone 30 may be operated at about 400-600 F. if mere dehydration of the coal in bed 20 at temperatures of 200-300 F. is desired. On the other hand, the temperature of zone 30 may be raised to l200-1500 F. in order to cause carbonization of the carbonaceous charge in bed 20, or to temperatures in the neighborhood of 2000 F. when it is desired to convert the solids of bed 20 into producer or water gas with the aid of air and/ or steam supplied through pipes [6. Bed 20 may also serve as a zone of mild oxidation at temperature conditions similar to those indicated above for preheating when a suitable amount of oxygen or air is added to the gas supplied through pipes l 6. In all these cases the temperature differential between zone 30 and bed 20 as well as the absolute temperature levels may be additionally controlled by choosing a suitable ratio of fresh carbonaceous solids feed to bed 20 to the combustion rate in zone 30.

As previously indicated, zone 30 may also be operated as a conversion or treating zone proper such as a carbonization or gasification zone rather than as a mere heat-generating zone. For this purpose, the dimensionsof zone 30 are increased in relation to chamber l0 and the linear velocity of the gases flowing through zone 30 is decreased so as to permit the treatment of a more substantial proportion of the total solids charge per unit of time at the conditions of zone 30. For example, zone 30 may have about the diameter and about the height of chamber [0 and the linear gas velocity within zone 30 may be about 2-4. ft. per second as compared with a gas velocity of about 0.5-1.5 ft. per second in bed 20, the relative and absolute temperatures in zone 30 and bed 20 being controlled by the supply of oxygen and, preferably, of extraneous fuel, in cooperation with a control of the ratio of fresh solids feed to bed 20 and zone 30.

The temperature conditions and reactants required for these various conversions are those known in the art and need not be here specifically enumerated. However, it is noted that Whenever a substantial amount of condensible volatile products such as tar is produced in zone 30 the vapors of such condensible products should be separated from entrained solids in conventional gas-solids separators, preferably at a temperature close to that of zone 30, prior to the return of the solids to bed 20 in order to prevent condensation of tar or the like in bed 20. Whenever zone 30 serves as a conversion zone, the

carbonaceous; charge issimultaneously dried and preheatedand, if desired, mildly oxidized vin n sorhf cases, it desirable m ;11 t insulate zone 30 ,as'indicat'ed at 3| in order to increase the. temperature differential between zone".'30"an'd bed 20...} 'This'insulation is'ofpartic'ular .valuefduring'the starting up period of the, process' whichfrequires preheating of the fiuidssuppliedthrough line 5 beyond theignitiont'emperature of thefuel used in zone30. While I have shown combustion zone 30 as a vertical cylinder and this is the preferred'embodiment of my invention, zone 30 may be arranged horizontally or it may have the shape of tube bundles or any other suitable shape without deviating from the spirit of my invention.

It will be understood that my process may be made fully continuous by continuously feeding and withdrawing carbonaceous solids through lines I and 9, respectively, and'continuously feeding fluids supporting the invention through line 5.

My invention will be further illustrated by the following specific example.

Example In order to preheat two tons per hour, of a bituminous coal of about in. average particle size containing about 5% of water and having a plasticizing temperature of about 700 F. and an incipient carbonization temperature of about 750 F., from 60 F. to 600 F. the process of the invention may be carried out at the conditions given below.

While the foregoing description and exemplary operations have served to illustrate specific applications and results of my invention, other modifications obvious to those skilled in the art are within the scope of my invention. Only such limitations should be imposed on the invention as are indicated in the appended claims.

The present application is a division of Serial No. 699,949 filed September 28, 1946, now Patent No. 2,582,710.

What is claimed is:

1. Apparatus for treating carbonaceous solids which comprises a vertical treating chamber, a horizontal plate in the lower portion of said chamber said plate being provided with orifices adapted to permit the passage of finely divided solids, a second vertical chamber of about /z-fi the height and e the diameter of said first named chamber, arranged within said first named chamber, the lower portion of said second chamber protruding through said plate and opening into the space of said first named chamber below said plate and the upper portion of said second chamber extending above said plate into said treating chamber and opening into said mme-6% treating chember; heads for passing gas fup= wardiy into the lower opening 'Of said second chamber, means arranged above said plateior distributing a gas' within'said treating chamber above said plate, means idr supplying a gas" to said treatingchamber in a lower portion ofthe spaceiibeiow said plate; means for supplying fine- 1y divided solids'to said. treating, chamber, means for withdrawing firiely divided. solid mm' said treating chamber at a; point above Said plate and 10 means for withdrawing" gases cdrifying entraiiied solids from an upper portidn of said treating chamber. V V i 3; Abrgara-tusas ciai fified in 0 mm 1" wfierein saidoiifices are adjustable A e V HOME-R; z. MARTIN.

I REFERENGES CITED The: foiiewmg references are of record iii the file (if fil'iis ii'afifitzf V UNITED STATES PATENTS lVu nnber- M Name Date 2 -,391, 44; "McAfe Dee. 25, 1945 2,411,592 Reeves Nov. 26,- 1946 

1. APPARATUS FOR TREATING CARBONACEOUS SOLIDS WHICH COMPRISES A VERTICAL TREATING CHAMBER, A HORIZONTAL PLATE IN THE LOWER PORTION OF SAID CHAMBER SAID PLATE BEING PROVIDED WITH ORIFICES ADAPTED TO PERMIT THE PASSAGE OF FINELY DIVIDED SOLIDS, A SECOND VERTICAL CHAMBER OF ABOUT 1/2-1/10 THE HEIGHT AND 1/2-1/10 THE DIAMETER OF SAID FIRST NAMED CHAMBER, ARRANGED WITHIN SAID FIRST NAMED CHAMBER, THE LOWER PORTION OF SAID SECOND CHAMBER PROTRUDING THROUGH SAID PLATE AND OPENING INTO THE SPACE OF SAID FIRST NAMED CHAMBER BELOW SAID PLATE AND THE UPPER PORTION OF SAID SECOND CHAMBER EXTENDING ABOVE SAID PLATE INTO SAID TREATING CHAMBER AND OPENING INTO SAID TREATING CHAMBER, MEANS FOR PASSING A GAS UPWARDLY INTO THE LOWER OPENING OF SAID SECOND CHAMBER, MEANS ARRANGED ABOVE SAID PLATE FOR DISTRIBUTING A GAS WITHIN SAID TREATING CHAMBER ABOVE SAID PLATE, MEANS FOR SUPPLYING A GAS TO SAID TREATING CHAMBER IN A LOWER PORTION OF THE SPACE BELOW SAID PLATE, MEANS FOR SUPPLYING FINELY DIVIDED SOLIDS TO SAID TREATING CHAMBER, MEANS FOR WITHDRAWING FINELY DIVIDED SOLID FROM SAID TREATING CHAMBER AT A POINT ABOVE SAID PLATE AND MEANS FOR WITHDRAWING GASES CARRYING ENTRAINED SOLIDS FROM AN UPPER PORTION OF SAID TREATING CHAMBER. 